Holograms have long been used for security to indicate that a document or product is authentic and to increase the attractiveness of goods such as lottery and entertainment/sporting event tickets, product packaging such as for DVDs, event programs, calendars and magazines. Indeed, methods and apparatuses for creating holographic optical elements on a recording medium, i.e., substrate, to create an overall optical illusion have been known in the art for some time. Generally, a hologram is created by splitting a laser into two beams, an object beam and a reference beam. The object beam is spread, reflected off of an object and directed onto the recording medium. The reference beam travels directly onto the recording medium. When the two laser beams reach the recording medium, their light waves intersect and interfere with each other. It is this interference pattern that is imprinted on the recording medium to produce the hologram on the substrate.
A more recent development in holographic imaging technology has been the ability to create two or more different holographic images on a single sheet. Such known methods utilize a process/technique called mechanical recombination, where a first holographic image is printed on a substrate and that image is physically combined with a substrate having another holographic image. This process involves physical/manual manipulation of the holographic printing/imaging apparatus between the printing of each individual holographic image, and physical combining of the images in order to produce a sheet having multiple different holographic images.
As will be readily appreciated, such mechanical recombination is slow and laborious, and may suffer from misalignment or registration issues. In particular, such a process may result in improper registration or placement of the different holographic images with respect to one another or with respect to other areas of the sheet which are configured to accept subsequent ink printing or other holographic image. Moreover, holographic sheets produced through mechanical recombination often do not have a smooth surface, as the edges of each holographic image can be felt by running a finger over the surface, which is undesirable.
In view of these shortcomings, there is a need in the industry for a method of creating a sheet having a plurality of different holographic images that obviates the need for mechanical recombination, and which is faster and more efficient than known processes.